1. Field of the Invention
The present invention relates to a master cylinder for a brake system, and more particularly, to a a master cylinder for a brake system that can improve a braking feeling.
2. Description of the Prior Art
In a vehicle's hydraulic brake system, a master cylinder is an apparatus that generates hydraulic pressure according to the pedaling of the driver and sends the hydraulic pressure that is necessary to the brakes that are installed in the wheels of the vehicle in order to perform the braking operation.
FIG. 1 illustrates a general tandem type master cylinder. Referring to the drawing, the master cylinder includes a first piston 3 and a second piston 4, which are installed in a bore 2 of a cylinder body 1 in series to be moved forwards and rearwards, and the interior of the bore 2 is divided into a first liquid pressure chamber 5 and a second liquid pressure chamber 6 by the first piston 3 and the second piston 4.
According to the master cylinder, the first piston compresses the brake liquid in the first liquid pressure chamber 5 while being moved forwards in the direction of an arrow through the pedaling of the driver, the pressure of the brake liquid in the first liquid pressure chamber 5 presses the second piston 4, and the second piston 4 compresses the brake liquid in the second liquid pressure chamber 6. The brake liquid in the first liquid pressure chamber 5 is supplied to a wheel brake for braking two wheels through the first brake liquid discharge opening 7, and the brake liquid in the second liquid pressure chamber 6 is supplied to a wheel brake for braking the other two wheels through the second brake liquid discharge opening 8.
The master cylinder includes a brake liquid port 9, which is connected to a reservoir R provided above the cylinder body 1, and in which the brake liquid is stored to supply the brake liquid to the liquid pressure chambers 5 and 6. Because the brake liquid port 9 simply functions as a passage for the brake liquid between the master cylinder and the reservoir, it cannot effectively control the flow of the brake liquid according to the pressure of the liquid pressure chambers that are necessary when a prompt braking operation is required.
For example, the pressure of the liquid pressure chambers 5 and 6 should be increased by closing the brake liquid port 9 while the piston is moved forwards in order to perform a braking operation, and because the brake liquid in the liquid pressure chamber is substantially discharged to the reservoir such that the liquid pressure chamber is not sealed in the piston movement section from an initial standby position to a position where the brake liquid port 9 may be closed, a braking operation is not performed in the section.
The section in which a braking operation cannot be performed is called a lost travel. The lost travel is present in order to prevent a phenomenon in which a braking pressure is generated irrespective of the intention of the driver as a caliper pad is moved rearwards or a peripheral temperature rises. For example, a drag due to an abnormal expansion of the fluid in the liquid pressure chamber.